Double-difference Location Method Research Articles

Deep seismogenic tectonics of Yangbi MS6.4 on 21 May 2021 in the SE margin of the Tibetan plateau from earthquake sequence relocation, stress field and seismic anisotropy

The MS6.4 earthquake occurred in Yangbi County, Yunnan Province, China, on 21 May, 2021. The earthquake is located on the west side of the Red River fault, the western boundary of the Sichuan-Yunnan block in the SE margin of the Tibetan Plateau. The Yangbi MS6.4 earthquake has aroused great concern due to its unique geographical location and frequent strong earthquakes in Yunnan. In this study, a total of 4695 local earthquakes of the Yangbi MS6.4 earthquake sequence are relocated using the double-difference location method, including the mainshock source location of 99.879°E, 25.687°N, and depth of 9.67 km. The mainshock has a moment magnitude of 6.1, and one of the fault-plane solutions is 137°, 83° and − 163° in strike, dip, rake respectively. Combined with the relocation and focal mechanism solutions results, it is suggested that the seismogenic fault of the Yangbi MS6.4 earthquake is a NW-SE trending fault on the southwest side of the Weixi-Qiaohou fault (WQF), with high dip of SW, which is a previously-unknown blind fault. The regional 2D stress field shows that the principal compressive stress around the Yangbi earthquake is NNW-SSE and nearly N-S direction, which appears to be deflected counterclockwise by a small angle on its east side and changed to N-S and NNE-SSW direction on its west side, while both the north and south sides of the Yangbi earthquake show directional coherence. Strong differential deformation distorts in the upper crust to the northeast of the seismic source as reflected by tectonic stress field and the upper crust seismic anisotropy, indicating strong influence of Lijiang-Xiaojinhe fault (LXF). The stress field in the source area is jointly controlled by southeastward movement of southeastern margin of Tibetan Plateau, the northeastward movement of Indian plate and the differential movement between the different tectonic blocks.

Cross-related microseismic location based on improved particle swarm optimization and the double-difference location method of jointed coal rock mass

The location algorithm is the core of microseismic monitoring, and the location results directly influence the effectiveness of the subsequent source analysis. We introduced the double-difference (DD) location method in seismic location into microseismic monitoring. We built a travel time equation of the layered velocity model using the ray-tracing theory and analyzed the waveform cross-correlation of the microseismic data using a generalized cross-correlation (GCC) technique. The improved particle swarm algorithm was successfully conducted to improve the randomness of the initial location. We then adopted the DD location method to precisely locate the secondary location, and it showed better location accuracy and computational efficiency than that by a traditional location algorithm based on the simplified geological model. The theoretical simulation and practice results in deep mining show that the proposed method significantly increased the location accuracy, and the results were concentrated and consistent with the field results. Moreover, we verified the importance of the velocity model for location accuracy. This algorithm also increased the ease of identifying fracture regions, providing the necessary theoretical and technical support for the source location of the jointed coal rock mass in deep mining.

Analysis of the Badong Ms5.1 earthquake source characteristics

The mainshock location of the Badong Ms5 .1 earthquake is determined using four location methods: the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using the double difference location method. The results indicate that aftershocks are distributed as bands along the NEE direction and that the aftershocks 1 month after the mainshock, which are mainly distributed in the west of the mainshock and near the Gaoqiao fault, are shallow earthquakes within 5 km; the depth of each aftershock after one month is deeper, and two distinct fault planes, for which the geological occurrence is similar to the Gaoqiao and Zhoujiashan-Niukou fault, are shaped. The frequency-spectrum analysis of the recorded waveform in 12 seismic events indicates that the corner frequency of the mainshock is significantly lower than that of its aftershock and is also lower than a tectonic earthquake of the same magnitude. We considered that this result is related to the constraint of the parameter calibration relationship in the focal spectrum and the lithology change due to water erosion. Combined with the focal mechanism and geological tectonic setting, we conclude that the occurrence of the earthquake is related to the activity of the Daping and Gaoqiao fault and is a reservoir-induced tectonic seismicity.

Detection of metastable olivine wedge in the western Pacific slab and its geodynamic implications

Seismic tomography and numerical simulations show that the western Pacific slab bends horizontally when it reaches the boundary between the upper mantle and lower mantle beneath northeast Asia. It is expected that a metastable olivine wedge (MOW) exists in the cold core of the slab because of a delayed phase transition from olivine to its high-pressure polymorphs. However, it is still debated whether the MOW actually exists or not, and even if it exists, its physical properties, such as seismic velocity and density, are still unclear. In this work we use high-quality arrival-time data of 17 deep earthquakes occurring within the Pacific slab under northeast Asia to study the detailed structure of the slab. The deep earthquakes are relocated precisely by applying a modified double-difference location method to arrival-time data recorded at both Chinese and Japanese stations. Based on the precise hypocentral locations, a forward modeling method and differential travel-time residuals data are used to estimate seismic velocity within the deep source zone, which can decrease or remove the influence of ambient velocity heterogeneities. Our results show that the MOW does exist within the Pacific slab under northeast Asia, and the MOW has a mean velocity anomaly of 7–9% lower than the iasp91 Earth model. The existence of MOW in the slab has important geodynamic implications. It can reduce the speed of slab subduction and affect the generation of deep earthquakes.

A detailed analysis of microseismicity in Samos and Kusadasi (Eastern Aegean Sea) areas

A detailed investigation of microseismicity and fault plane solutions are used to determine the current tectonic activity of the prominent zone of seismicity near Samos Island and Kusadasi Bay. The activation of fault populations in this complex strike-slip and normal faulting system was investigated by using several thousand accurate earthquake locations obtained by applying a double-difference location method and waveform cross-correlation, appropriate for areas with relatively small seismogenic structures. The fault plane solutions, determined by both moment tensor waveform inversions and P-wave first motion polarities, reveal a clear NS trending extension direction, for strike slip, oblique normal and normal faults. The geometry of each segment is quite simple and indicates planar dislocations gently dipping with an average dip of 40–45°, maintaining a constant dip through the entire seismogenic layer, down to 15 km depth.

Fault orientations in the upper crust beneath an intraplate active zone in northern Egypt

The present study aims to demarcate the active fault orientation in the upper crust of Dahshour Seismic Zone (DSZ) in Northern Egypt, and its relation to the regional tectonics. High-resolution earthquake relocations and focal mechanism solutions were determined using the double-difference location method and the forward modelling of the amplitude spectrum constrained with P-wave polarities, respectively. Up to 244 earthquakes were relocated by measuring differential travel times between events, as obtained from cross-correlation waveform analysis. The relocated hypocenters exhibited a seismogenic crust of 6-km thickness (most hypocenters have a focal depth of 18 to 24 km). Incorporation of hypocentral distributions and focal mechanisms depicts distinct fault planes trending to the NW and ENE to EW, randomly distributed in the whole dislocation zone. The reactivation of these pre-existing faults is attributed to the northern Red Sea-Gulf of Suez rifts and the closure of the Neotethys, respectively; implying a potential impact of the regional tectonic process on the deformation acting in the upper crust of the local seismogenic zones of northern Egypt.

High-resolution fault image from accurate locations and focal mechanisms of the 2008 swarm earthquakes in West Bohemia, Czech Republic

We have analyzed 463 micro-earthquakes in the magnitude range from 0.5 to 3.8 that occurred during the 2008 earthquake swarm in West Bohemia, Czech Republic, in order to screen the detailed structure of the focal zone situated at depths between 7 and 11km. The double-difference location method was applied to records of 22 local seismic stations with an epicentral distance of less than 25km in order to retrieve highly accurate locations of hypocenters with an accuracy of less than 20m. The hypocenters are well-clustered and distinctly map the system of activated faults. The fault system has a complex geometry being composed of several fault segments with different orientations. Some of the segments intersect each other. The orientations of the segments coincide well with the focal mechanisms. We have introduced and evaluated the so-called fault instability of the individual fault segments. The fault instability ranges from 0 (most stable faults) to 1 (most unstable faults) and measures the susceptibility of the fault to be activated under specified stress. In the West Bohemia focal zone, two fault segments are optimally oriented with respect to the tectonic stress being characterized by an instability value higher than 0.9. Tractions on these fault segments are concentrated in the Mohr's diagram in the area of validity of the Mohr–Coulomb failure criterion and the associated micro-earthquakes are mainly shear. The other fault segments are slightly misoriented with instability values between 0.7 and 0.9, and the shear traction is significantly lower. These earthquakes are probably more tensile and activated most likely by the local redistribution of Coulomb stress during swarm activity.

Seismicity within the actively deforming Eastern Sierras Pampeanas, Argentina

SUMMARY The Eastern Sierras Pampeanas of central Argentina have been interpreted by previous studies to represent the easternmost expression of continental deformation resulting from the flat-slab subduction of the Nazca Plate beneath the South American Plate. Yet, the seismic activity and deformation of this area, as well as its relationship to subduction more than 700 km to the west, are poorly understood. Using seismic data recorded by the Eastern Sierras Pampeanas broadband seismic array between 2008 August and 2009 August, we identified and located 445 local crustal earthquakes, most with magnitudes of 2.5 or less. We employed a double-difference location method to clarify the hypocentral distribution of local seismicity and to define zones of both clustered and diffuse seismicity. The relocated events define active structures in the region, including a horizontal zone of seismicity between 15 and 25 km depth, a prominent west-dipping structure beneath the central ranges and a vertical structure along the eastern margin of the study area. Overall, seismicity in this region during the study period is constrained to the upper ∼25 km of the crust and is mostly concentrated along minor structures and not along the major range-bounding faults. Focal mechanism solutions from the nine clearest events show mainly normal deformation with an oblique component and E–W oriented P-axes that likely result from shortening along structures with oblique orientations to the direction of plate convergence. This is the first seismic study to document that the Eastern Sierras Pampeanas are actively deforming in response to compression from the convergent margin.

High-resolution Earthquake Relocation in the New Madrid Seismic Zone

Other| March 01, 2010 High-resolution Earthquake Relocation in the New Madrid Seismic Zone Meredith Dunn; Meredith Dunn Center for Earthquake Research and Information University of Memphis 3890 Central Avenue Memphis, Tennessee 38152 U.S.A. capowell@memphis.edu (C. A. P.) *Now at Hess Corporation, Houston, Texas. Search for other works by this author on: GSW Google Scholar Steve Horton; Steve Horton Center for Earthquake Research and Information University of Memphis 3890 Central Avenue Memphis, Tennessee 38152 U.S.A. capowell@memphis.edu (C. A. P.) Search for other works by this author on: GSW Google Scholar Heather DeShon; Heather DeShon Center for Earthquake Research and Information University of Memphis 3890 Central Avenue Memphis, Tennessee 38152 U.S.A. capowell@memphis.edu (C. A. P.) Search for other works by this author on: GSW Google Scholar Christine Powell Christine Powell Center for Earthquake Research and Information University of Memphis 3890 Central Avenue Memphis, Tennessee 38152 U.S.A. capowell@memphis.edu (C. A. P.) Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2010) 81 (2): 406–413. https://doi.org/10.1785/gssrl.81.2.406 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Meredith Dunn, Steve Horton, Heather DeShon, Christine Powell; High-resolution Earthquake Relocation in the New Madrid Seismic Zone. Seismological Research Letters 2010;; 81 (2): 406–413. doi: https://doi.org/10.1785/gssrl.81.2.406 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Abstract We present high-resolution earthquake locations for the New Madrid seismic zone (NMSZ) using the double-difference location method. The NMSZ consists of four major arms of seismicity centered in the central United States and is one of the few places of concentrated earthquake activity far from a major plate boundary. The zone generates approximately 200 earthquakes per year. Double-difference relocation techniques prove well suited for this region because the distance between neighboring events is small and station coverage is relatively dense. The initial data set consists of 1,394 earthquakes recorded between 2000 and 2006 by 197 stations. The catalog contains approximately 67,000 P-wave and 54,000 S-wave observations, which yields 480,000 differential times. Waveform cross-correlation of P and S waves provides an additional 135,000 high-precision differential times. Relocated hypocenters align along individual segments of the seismic zone, providing a sharper image of the NMSZ faults. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural Heterogeneity in Northeast Japan and Its Implications for the Genesis of the 2004 and 2007 Niigata Earthquakes

Abstract We utilized 188,766 P -wave and 179,328 S -wave high-quality arrival-time data from 14,666 local earthquakes to determine the three-dimensional (3D) seismic velocity ( V P , V S ), V P / V S ratio, crack density ( e ), and bulk velocity ( V ϕ ) structures in and around the source areas of the 2004 and 2007 Niigata earthquakes (Japan Meteorological Agency magnitude [ M J ] 6.8) in Japan in order to understand the generation mechanisms of the Niigata mainshocks. The aftershock hypocenters were relocated by applying the double-difference location method simultaneously with the tomographic inversion, indicating a complicated fault system that includes not only two parallel dominant faults dipping to the northeast but also some conjugate faults crossing the Niigata mainshock hypocenters. In general, high velocity ( V P , V S ) with low e at 11 km depth is visible in the southeastern part of this area in contrast to anomalous low velocity with high crack density in the northwestern part along the Niigata-Kobe tectonic zone (NKTZ). These characteristics of the velocity and crack density are consistent with the spatial distribution of active faults along the NKTZ. The surface geological features that indurated pre-Neogene rock outcrops were observed in the southeastern area, whereas deep sedimentary basins were observed on the opposite side. Low V P and low V S zones with high V P / V S anomalies were imaged in and/or under the source areas, showing agreement with those revealed by previous studies. All the features of the velocity and V P / V S structures, together with the images of the crack density and bulk velocity, suggest the presence of fluids under the source areas. Such fluids might have weakened the mechanical strength of the fault zone of the source areas, thus triggering the 2004 and 2007 Niigata earthquakes. Our present study, together with other recent tomographic images, reveals that fluids penetrated into the source rocks from the lower crust and uppermost mantle as a result of dehydration of the subducting Pacific slab and thus may play a key role in the genesis of these large crustal earthquakes.

Relocation of Intermediate-depth Earthquakes beneath the NE Japan Arc by Double-Difference Location Method

We relocated interplate and intraslab earthquakes beneath the Tohoku district of NE Japan using the Double-Difference location method [Waldhauser and Ellsworth (2000)]. Relative earthquake arrival times were determined by waveform cross-spectrum analysis and catalog-picking data. Our relocations show that between 50 and 150 km in depth, most of the upper-plane seismicity occurs in the slab crust, and most of repeating earthquakes seem to occur along the upper boundary of the Pacific plate, where the intraslab seismicity is active. Obtained result shows that both the lower-plane and upper-plane seismicity are distributed unevenly in space. Moreover, there is a spatial correlation between clusters of upper-and lower-plane seismicity. If intermediate-depth earthquakes are caused by dehydration and/or CO2-bearing devolatilization of hydrated minerals [Kirby et al. (1996), Kirby et al. (2004), Peacock (2001), Seno and Yamanaka (1996), Yamasaki and Seno (2003)], the present result suggests that hydrated and/or carbonate minerals are distributed unevenly but in common in both the crust and deeper mantle of the slab. In the southern part of Tohoku district, where some seamounts subduct, seismicity between upper and lower seismic planes is active. If the hydrated and carbonate minerals are abundantly distributed in the slab crust and the slab mantle due to the volcanic activities of the seamount formation, dehydration and devolatization of these minerals may cause intraslab earthquakes.